A failure in a poorly designed test reactor isn't a great argument against nuclear power

I'm not making this comment to disagree with your point, but the failure of the SL-1 reactor strikes me as an engineering and process failure more than anything else. The reactor was not designed in a safe fashion, probably because it was designed as a test bed for reactors that could be deployed via airplanes to the Arctic circle. The fact that an engineer was even able to fully remove a control rod, and the fact that removing that control rod lead to a fatal steam explosion make me think that they really tried too hard when they removed weight and volume from the reactor design.

In well designed safety-critical systems, human error should not be able to cause any form of bodily harm. I don't think it's a great idea for a private company to be running nuclear reactors on Earth to power something as trivial as a data center (investing in storage + local solar/wind/geothermal/hamster wheel velodrome seems like a more efficient use of resources for one thing), but I also don't think that SL-1 is the best example to cite here.

As an aside, my high school Physics teacher went on a long diatribe about how the three SL-1 casualties were the only humans ever killed as the direct result of nuclear fission in the context of a nuclear reactor. Looking back on it, I think she was splitting hairs a bit, but it is an interesting point to make.

SL-1 can't happen in a modern reactor design. In fact, it probably could never have happened in any non-test bed reactor. The issue was cause by an actual human pulling the control rod physically, from what I can tell. That's just not a thing done with operating reactors I'm pretty certain. There are also a ton more precautions built in than they had, as well as better protocal and understanding of the mechanics.

Well you know how that goes.

I don't, please elaborate.